Limit and integral

Calculus Level 3

lim n 0 1 x n x d x = ? \large\lim _{ n\rightarrow \infty }{ \int _{ 0 }^{ 1 }{ \left| { x }^{ n }-\left| x \right| \right| } } \ dx = \ ?


The answer is 0.5.

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2 solutions

Tanishq Varshney
Mar 18, 2015

As the limits range from 0 to 1.So x x is a number between 0 and 1.

lim n x n 0 \displaystyle \lim_{n\to \infty} x^{n} \rightarrow 0

So the integral reduces to 0 1 x . d x \displaystyle \int^{1}_{0} |-x|.dx

x 2 2 \frac{x^2}{2} limits from 0 to 1

= 0.5 =0.5

U can also try this

Lucas Tell Marchi
Apr 12, 2015

See, the integration is inside the interval ( 0 , 1 ) \left ( 0,1 \right ) . But in this interval we have

0 < x < 1 0 < x n < x 0 < x < 1 \;\; \Rightarrow \;\; 0 < x^n < x

And, therefore, as x > 0 |x| > 0 for x x in our interval,

x n x < 0 x n x = x x n x^n - |x| < 0 \;\; \Rightarrow \;\; |x^n - |x|| = x - x^n

Therefore the integral becomes

0 1 x n x d x = 0 1 ( x x n ) d x = 1 2 1 n + 1 \int_{0}^{1} |x^n - |x|| \; \mathrm{d}x = \int_{0}^{1} \left (x - x^n \right ) \; \mathrm{d}x = \frac{1}{2} - \frac{1}{n+1}

And

lim n ( 1 2 1 n + 1 ) = 0.5 \lim_{n\rightarrow \infty} \left (\frac{1}{2} - \frac{1}{n+1} \right ) = 0.5

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